Abstract:

Pollen grains of 6 genera, including 36 species, of the Betulaceae, were examined

under LM, SEM and TEM.Their morphological characters are described and three types of

pollen are distinguished here. The evidence from pollen morphological characters does not

support Hutchinson's (1973)and Dahlgren's (1983)treatments which divided the Betulaceae

into two families: Corylaceae ( including Corylus, Ostryopsis, Carpinus  and Ostrya) and

Betulaceae (including Alnus and Betula). The author agrees with Abbe's (1974)division of

the Betulaceae into three tribes with one modification that Ostryopsis is transferred from the

tribe Coryleae to the tribe Carpineae. The limits of the three tribes presented here are the same

as Kuprianova's (1963) treatment in which she divided the Betulaceae into three families. It is

more reasonable to treat Kuprianova's families as tribes. Pollen morphological characters of

the three tribes of the Betulaceae are described as follows:

      1. Tribe Betuleae (including  Alnus  and  Betula):  Pollen grains are triporate or

stephanoporate and oblate, suboblate or spheroidal. Sometimes the exine has arci and the

ektexine thickens in the apertural region; the sculpture of exine is slightly rugulate under

scanning electron microscope (SEM) ; the exine structure is four-layered: tectum,

columellae, footlayer and endexine. The columellae are columellate, the endexine thickens in

the apertural region and sometimes it is separated from the footlayer to form vestibulum.

     2. Tribe Coryleae (only Corylus): Pollen grains are triporate and suboblate. The exine

has no arci and the ektexine does not thicken in the apertural region; the sculpture of exine is

slightly rugulate under SEM; the exine structure is five-layered: granular layer, tectum,

columellae, footlayer and endexine. The tectum is vovered with a granular layer, the

columellae granular and the endexine thickens but is not separated from the footlayer in the

apertural region.

     3. Tribe Carpineae (including  Ostryopsis, Carpinus and  Ostrya): Pollen grains are

mostly triporate and suboblate. The exine has no arci and the ektexine does not thicken in the

apertural region; the sculpture of exine is slightly rugulate under SEM; the exine structure is

five-layered which is the same as those of the Coryleae. The tectum is covered with a

granular layer, the columellae are columellate and the endexine is neither thickened nor sepa-

rated from the footlayer in the apertural region. The operculum exists on the top of aperture

membrane.

Key words: Betulaceae, Pollen morphology